The present invention relates to polymer-liquid crystal mixtures, and more specifically to forming of polymer architectures such as polymer micro-walls using polymerization in the liquid crystalline matrix with spatially distorted director fields.
The electro-optic properties of polymer-liquid crystal mixtures have made them useful as elements of various optical devices. Depending on the relative polymer concentration in the mixture, different types of devices have been demonstrated. When the concentration of polymer significantly exceeds that of the liquid crystal (LC), a polymer dispersed liquid crystal (PDLC) type of device is realized, where the LC is suspended in the form of small droplets in a surrounding polymer matrix. Light, heat, or solvent evaporation can be utilized to induce the desired phase separation. Light scattering characteristics of the device are dependent upon the orientation of molecules within the LC. In a second type of device, the concentration of polymer is significantly lower than that of the LC. In this case, a polymer stabilized type of device is realized. The LC is mixed with a pre-polymer (monomer), which is then polymerized. Polymerization of the monomer creates a polymer network which stabilizes the LC structure, enabling, e.g., creation of bistable LC displays.
When concentrations of the polymer and the LC are roughly of the same order of magnitude, it is possible, by implementing a holographic two-beam recording technique, to form an inhomogeneous periodic morphology which consists of a cross-linked polymer network with embedded LC droplets. This is described by Pogue et al. in SPIE, 3475, pp. 2-11 (1998). Large droplet size contributes significantly to unwanted light-scattering, and it is therefore desirable to reduce the size of the droplets as much as possible. As shown by Kim et al., Appl. Phys. Lett. 72(18), pp. 2252-2253 (1998), it is possible to directionally phase-separate the LC and polymer components in a high-voltage electric field using lithographic patterning of electrodes on a confining substrate. A difference in dielectric permittivity of the components plays a role in the phase separation.
A technique for the design of switchable diffractive elements with a memorized structure is needed. Shorter switching times and less light-scattering are desired. Reliable techniques for producing polymer architectures such as walls at micron scales would be advantageous for stabilizing the LC structure, reducing the light scattering and switching times. The polymer architectures can be used by themselves (by washing the LC out of the sample, e.g., in micro-mechanical and in micro-optical devices).